Merge main catalogs
When I moved to Lightroom Classic, it started using a new catalog instead of automatically important the old one, and in fact started scanning my SSD for photos. I was really just playing around, so didn't pay much attention--I just kept using the old LR (equivalent to the new "Classic"; not the new cloud-based CC). Now I'd like to move over to Classic and I find myself with two catalogues:

There is some redundancy. Whenever there's redundancy, I'd like to keep the version in the older catalog. What's the best strategy for merging them?
Thanks.
